The present invention relates to a cutter for a raise boring head. The cutter is rotatable about a center axis and mounted, via a shaft of the cutter, in a saddle secured to the raise boring head. The shaft has ends that are secured to the saddle by fastening means. Bearing means are provided between the shaft and a hub of the cutter in order to make it possible for the hub to rotate relative to the shaft. Sealing means between the shaft and the hub, and bore/hole means for introducing lubrication means into the interior of the cutter are provided. An expansion plug is mounted in the bore means. The expansion plug is designed to accommodate lubrication means that enters into the bore means from the bearing means. A stopper means is provided in the bore means. The invention further relates to a stopper means and a method of preventing mud from entering into a cutter.
When cutters of the type mentioned above are working it is necessary that the bearing means are embedded in a lubricant, preferably grease, i.e. the space between the shaft and the cutter is filled with grease. This is done in order to minimize the friction when the hub is rotated relative to the shaft. By having a low internal friction in the bearing means the life of the cutter is kept at an acceptable level. When the cutter is subjected to a heavy load, much heat is generated when the hub is rotated relative to the shaft and by friction when the cutter works the rock. Due to the heat generation the grease expands and the internal pressure of the cutter rises. Under such conditions it occasionally happens that the internal pressure of the cutter reaches a level where the sealing means are not able to withstand said internal pressure, i.e. the sealing means collapses and the grease emerges from the bearing means. It is readily understood that if the sealing means collapses then the cutter will rapidly break down.
In our SE-B-501 854 a cutter for a reaming head is provided with means to avoid the above-mentioned drawbacks. Said reference is incorporated in the present description by reference. However, it has turned out that during normal generally dry working conditions, mud has a tendency to clog the exit to the outside of the cutter. The clogged mud assume properties similar to concrete. This means that the escape route of the grease becomes blocked and that regreasing has to be preceded by a thorough cleaning in order to facilitate dismounting of a retainer plug.
In our U.S. Pat. No. 4,448,271 a mounting system for a saddle is described to which the present invention relates.